[unreadable] KLF6 is a tumor suppressor gene that is frequently altered in ganstrointestinal tumors (colon, liver, stomach). The molecular mechanism of KLF6 tumor suppression is not well understood. A major role of many other tumor suppressors is to govern the cellular response to DNA damage. In principle, DNA damage can lead to cell cycle arrest and DNA repair or, if damage is beyond repair, apoptosis. Both outcomes help to preserve genomic integrity of the organism. The possibility that KLF6 is important in these processes has not been explored. The KLF6 gene produces several gene products by alternative splicing. The full-length form, KLF6F and a shorter version with an altered carboxy terminus, KLF6V1 are the subject of this proposal. [unreadable] Preliminary data by the applicant suggests a role for KLF6F in regulating the cellular response to DNA damage: (i) Cell cycle arrest in response to DNA damage is impaired after downreglation of KLF6F by siRNA. (ii) KLF6F is induced in control cells in the setting of DNA damage with cell cycle arrest, (iii) KLF6 appears to be a substrate of ATM, a master regulator of the DNA damage response. [unreadable] Further preliminary data have delineated another possible role for the splice variant KLF6V1. Specifically, downregulation of KLF6V1 restored sensitivity to cisplatin in cells that were otherwise chemo-resistant. KLF6V1 appears to be constitutively expressed at high levels in cancers of the colon, liver, and stomach, suggesting that it may confer resistance to apoptosis, a hallmark of cancer. [unreadable] To define the role of KLF6F and KLF6V1 in DNA repair and apoptosis, our specific aims are: [unreadable] Aim 1: Investigate the response to DNA damage in cells that are null for KLF6 or harbor mutations that have been identified in human gastrointestinal cancer. [unreadable] Aim 2: Characterize ATM dependent degradation of KLF6F after lethal DNA damage and investigate how this determines KLF6F activity, (a) Test whether KLF6F is a direct substrate of ATM and characterize functional and physical interactions, (b) Create a degradation-resistant mutant to: (i) identify the region(s) of KLF6F responsible for its degradation using KLF6F truncation mutants and (ii) characterize posttranslational modifications that lead to degradation using mass spectrometry. (c) Test whether KLF6F degradation reflects its activation or inactivation using the degradation-resistant mutant. [unreadable] Aim 3: Explore whether the main KLF6 splice variant KLF6V1 is anti-apoptotic and confers resistance to chemotherapeutic agents, (a) Determine the impact of downregulation of KLF6V1 on DNA damage dependent apoptosis; (b) Test whether the anti-apoptotic activity of the KLF6V1 is mediated by c-FLIP. [unreadable] The proposed research plan will serve as a paradigm to train the applicant in the basic investigation of mechanisms of apoptosis, DNA damage signaling, carcinogenesis, and chemotherapy resistance. The proposed training is further enhanced by the selection of a mentor and consultants with backgrounds in hepatology, cancer research, basic genetics, and biochemistry, and by an intense didactic curriculum. [unreadable] The proposal is aimed at preparing the applicant in the responsible conduct of research with a disease focus on basic investigations in gastrointestinal malignancies [unreadable] [unreadable]